Telephone paging systems typically employ one or more paging speakers (driven by an attendant speaker amplifier) that are distributed throughout the respective paging zones served by the system. Because the audio (paging voice) signals are sourced from telephone signalling components, e.g. a desktop console or handset, the signals are of relatively low energy content and therefore require substantial amplification in order to successfully drive one or more paging speakers served by the system to a dB level that will be audible to paged personnel. The required power boost of telephone-sourced paging signals has been conventionally accomplished using a (relatively inefficient) class A speaker amplifier in the signal flow path from the telephone equipment sourcing the audio signals and one or more paging speakers.
Unfortunately, due to its relatively low efficiency, the audio class A amplifier dissipates a substantial amount of I.sup.2 R power as heat. As a consequence, the amplifier must be fabricated using large components and be connected to a relatively massive heat sink, which adds to the size and cost of the paging speaker components. Now, although another class of (audio) amplifier, such as a class D amplifier, may be more efficient, the performance of its associated audio output filter (to which one or more paging speakers are coupled as the output load) is highly dependent upon the output load. Therefore, for a given load the parameters of the (inductive and capacitive) components of the filter are tailored to optimize filter performance (maintain a flat frequency response). Unfortunately, in any given paging speaker installation, the number and size of paging speakers to be driven by the speaker amplifier may vary, so that setting the parameters of the class D amplifier output filter to a prescribed load specification may prove inadequate and distort the audio signals supplied to a speaker configuration different than for which the filter was originally designed. Thus, the inefficient class A paging amplifier circuit has continued to be used as the accepted paging speaker amplifier configuration.